Internalizing disorders, consisting of syndromes of anxiety and depression, represent common, debilitating conditions, the etiology of which is not well understood. Neuroscientists have developed dimensional assessment instruments and psychological tasks that probe negative valence systems as alternative phenotypes to clinical symptoms. Such alternative phenotypes are under consideration for use in the NIMH's Research Domain Criteria (RDoC) project. However, little is currently known regarding their genetic basis and how that relates to internalizing risk factors. This study will extend and deepen our understanding of the relationships between such alternative phenotypes and early manifestations of ID symptomatology. The approach will be to administer an informative suite of dimensional measures and experimental tasks to 500 pre-adolescent twin pairs from a large epidemiological sample. These subjects will also be assessed for current and lifetime internalizing psychopathology and a broad array of childhood risk/ protective factors. The expected outcome is to provide novel insights into the mechanisms by which genes and environment confer risk to internalizing disorders via these more basic phenotypes that putatively reflect underlying affective processing. PUBLIC HEALTH RELEVANCE: The high prevalence of anxiety and depressive disorders makes them a significant public health burden in the US. They often begin in childhood, but little is known about the mechanisms by which they affect some children but not others. This study, performed in pediatric twin pairs to understand genetic mechanisms, uses novel approaches to measure ways that children at risk for these conditions respond to negative emotional stimuli. Insights gained from this study can lead to significant advances in prevention and treatment for these conditions.